A boat hull requires periodic preventive and corrective maintenance to remove accumulated algae, organisms, and general dirt and other extraneous matter. The portion of a hull above the waterline is subject to other kinds of deterioration during normal operation of the craft, especially in a salt water environment, and this upper portion of a hull also requires occasional maintenance.
An owner of a pleasure craft may rent or own a boat slip in which to store his boat between outings. He may also own or have access to a hoisting assembly which typically is made of a hoist, cables, and slings to lift his boat out of the water for maintenance and repairs or simply to store the boat. By storing the boat out of the water, not only is the boat more easily maintained, it is also subjected to less attack from the elements and therefore requires less maintenance.
Large boats are more difficult to lift out of the water than smaller boats. To avoid the difficulty and expense (and possible damage to their boats) in routinely removing their boats from the water between outings, many owners of boats longer than 25 feet leave their boats in the water, typically at a marina, and periodically dry dock their boats at a commercial facility for periodic repair, painting, and other maintenance.
Commercial dry dock facilities are commonly of the submersible type. To dry dock a boat, the operator of the facility uses a relatively complex apparatus to submerge the dry dock, the craft is placed in position under its own power or by towing, and the submersible dry dock is lifted to lift the craft out of the water. Most submersible dry docks include various mechanisms such as doors, hydraulic or pneumatic cylinders, and other mechanisms. In addition to being expensive, such dry docks are subject to breakdown like any complex mechanical device.
For pleasure craft, owners or marine maintenance workers typically lift the boat out with a crane or hoist system, and set the boat on land on pods for support, where maintenance may be performed.
Other facilities simply lift the pleasure craft out of the water using a crane, hoist, or the like and transfer the vessel onto support pedestals where maintenance work is performed.
Consequently, there remains a need for a simple, affordable, dry dock apparatus that will allow the owners of relatively shallow-draft pleasure craft to reduce their maintenance costs, perform needed maintenance, and generally secure their boats on a routine basis without significant structural modifications to existing storage facilities such as marinas.
During further development of the invention disclosed in the above-mentioned application Ser. No. 08/294,253 now U.S. Pat. No. 5,549,070, it has been found that overland shipment of dry-dock can be simplified in certain circumstances by forming the dry-dock from two mirror-image halves. The whole dry-dock, formed as a single molding may present difficulties as a wide load in highway transit, and particularly in marina areas. There thus remains a need for a dry-dock that can be formed of mirror image halves that are easily assembled at the site of use, thus eliminating the "wide load" problem.
In northern freezing climates, pleasure craft are typically removed from the water because water expands as it freezes. This expansion creates extremely high crushing pressures on the hulls of the pleasure craft. Dry-docks may also find use in these freezing waters at the most beneficial time, the time in which the pleasure craft are removed from the freezing waters to protect them from the crushing ice forces. Thus, there remains a need for a means of absorbing the pressures exerted by frozen water surrounding the dry-dock.